Vegetation Inventory Project: City of Rocks National Reserve

Erixson, John; Cogan, Dan

City of Rocks National Reserve (CIRO) is located in south-central Cassia County, ID near the Utah border. The Reserve encompasses over 14,000 acres in the Albion Mountains near the village of Almo, ID. The unique geologic exposures, particularly the granitic spires, are renowned among rock climbers. Also present in the Reserve are many significant cultural resources, including the California Trail ruts and signatures, early homesteading and mining claims, and archaeological sites from the paleoindian to contact period. The area is considered to be within the traditional lands of the Shoshone-Bannock Tribe. CIRO vegetation includes unique mix of native montane woodlands, basin and range shrublands, and semi-native herbaceous vegetation. The Reserve has a moderate to high elevation and steep slopes allowing (min’-max’) for establishment and maintenance of subalpine fir (Abies lasiocarpa), limber pine (Pinus flexilis), and quaking aspen (Populus tremuloides) forests on mesic mountain ridges and slopes. Also runoff from exposed bedrock creates distinctive habitats and enhances support of extensive stands of singleleaf pinyon pine - juniper (Pinus monophylla and Juniperus spp.) woodland and curl-leaf mountain mahogany (Cercocarpus ledifolius) woodland and tall shrubland. As the elevation decreases and the terrain flattens, steppe shrubland vegetation characterized by sagebrush (Artemisia spp.), rabbitbrush (Ericameria spp. and Chrysothamnus spp.), antelope bitterbrush (Purshia tridentata), and several bunchgrass species become the dominant cover on deeper soils. Smaller but very important vegetation stands include wetland and riparian plant communities characterized by chokecherry (Prunus virginiana), Booth willow (Salix boothii), and gray alder (Alnus incana) shrublands and stands of Nebraska sedge (Carex spp.) herbaceous vegetation. Large fires in and around the Reserve have dramatically altered the landscape replacing burned pinyon-juniper woodland with rabbitbrush shrublands and non-native cheatgrass (Bromus tectorum) annual herbaceous vegetation. To better understand the plant community distribution the NPS Vegetation Inventory Program (NVIP) funded this inventory and mapping project. The Upper Columbia Basin Inventory and Monitoring Network (UCBN) coordinated this effort as part of a network-wide program. A three-year, three-phase program was initiated to complete the tasks of sampling, classifying, and mapping the plant associations and vegetation alliances within CIRO. Phase-one, directed by UCBN staff in conjunction with Northwest Management Incorporated (NMI), Idaho State University (ISU), and S.M. Stoller Corporation (Stoller) resulted in the plant association and vegetation alliance classification using the National Vegetation Classification System (NVCS). Vegetation classification was based on the 2009 field sampling of 190 representative classification plots located within the boundary of CIRO and adjoining Castle Rocks State Park. Analysis of the classification plot data by ISU and Stoller ecologists occurred in 2010. Through this process 35 distinct plant associations were identified as were two vegetation alliances. Vegetation alliance and plant association local descriptions and a field key to determine each association in the field are included in this report. Phase-two, directed by NMI and Cogan Technology, Inc. (CTI) resulted in creation of the digital vegetation and land use map and project geodatabase. Mapping was conducted primarily by interpreting vegetation-specific and non-vegetated site signatures from the 2009 National Aerial Imagery Program (NAIP) ortho-photo products. CTI reliably discerned 34 vegetation, 10 land use/land cover, and one geology/sparse vegetation map units. The mapping process relied on manual digitizing of homogenous photo-signatures supported by on-site verification. All interpreted data were converted to Geographic Information System (GIS) databases using ArcGIS software. The final